Second harmonic imaging of plants tissues and cell implosion using two-photon process in ZnO nanoparticles

The optical properties of colloidal ZnO nanoparticle (NP) solutions, with size ranging from several nm to around 200 nm, have been tailored to have high optical nonlinearity for bioimaging with no auto-fluorescence above 750 nm and minimal auto-fluorescence below 750 nm. The high second harmonic conversion efficiency enables selective tissue imaging and cell tracking using tunable near-infrared femtosecond laser source ranging from 750-980 nm. For laser energies exceeding the two-photon energy of the bandgap of ZnO (half of 3.34 eV), the SHG signal greatly decreases and the two-photon emission becomes the dominant signal. The heat generated due to two-photon absorption within the ZnO NPs enable selective cell or localized tissue destruction using excitation wavelength ranging from 710-750 nm.